To ensure proper nutritional support for newborn infants, many doctors and hospitals recommend the use of liquid pediatric nutritional products. Pediatric nutritional products are utilized when breast feeding is not possible for either medical and/or social reasons. Furthermore, even in cases where breast feeding is possible, some mothers prefer the convenience afforded by the use of pediatric nutritional products.
In response to the need for pediatric nutritional products soy and milk-based liquid foods have been developed for bottle feeding in conjunction with a rubber or latex nipple. Since the containers for these nutritional products should provide a twelve to eighteen month shelf life, a hermetic seal must be provided across the top of the container. A hermetic seal is one which when in place is impervious to microbiological intrusion and external influence. Presently, hermetic sealing is accomplished through the use of a glass container, to which is secured by vacuum closure a stamped steel cap having a pre-cut rubber or vinyl plastisol gasket. The sealed container is then subjected to temperatures above the ambient air temperature, and more specifically to retort conditions, during which the hermetic seal must survive sterilization of the nutritional product and the container. Since the glass container and the stamped-steel cap expand a similar amount and since a vacuum is present within the container, the hermetic seal is usually maintained during the sterilization process.
Due to concerns about material cost, container weight, and breakage, suppliers of nutritional products have sought to manufacture the product container from a plastic substance, such as polypropylene, which is relatively clear, optically, and cost effective as compared to glass. A problem arises in attempting to provide a cap for a plastic container, which cap still maintains a hermetic seal. Since it is difficult to maintain a vacuum in a plastic container, and conventional metal caps and plastic containers expand by a dissimilar amount, the prior art metal caps can not maintain a hermetic seal on plastic containers when subjected to retort conditions.
Another problem arises in that the heat during retort conditions causes polymer relaxation or shrinkage, especially in the upper neck portion of the container. Injection or extrusion molded plastic bottles are formed by stretching the polymer molecules. The introduction of heat causes those molecules to relax, so as to actually shrink the diameter of the neck. This shrinkage causes severe problems in maintaining a conventional metal cap on a plastic bottle. This shrinkage also prevents the use of a conventional plastic cap on a plastic bottle.
One approach to overcome these problems would be to apply a substantial amount of torque when initially capping the bottle. However, the amount of torque necessary to maintain a conventional cap on a plastic bottle is so high that a person would not be able to easily twist off the cap following retort. Another possible approach would be to fabricate a bottle from a plastic which does not shrink at retort temperatures and can maintain an internal vacuum without distortion, however, the cost of providing such a plastic bottle would is prohibitive.
Yet another possible approach to the providing of a hermetic seal to a plastic container would be to utilize a barrier membrane, such as aluminum foil, such that the integrity of the seal is independent of the closure or cap. This primary membrane seal or foil would be protected from accidental or premature puncture by an overcap of conventional design. One type of foil seal is the type which is peelable. However, in dealing with nutritional products subject to spoilage, peelable seals are not optimal for maintaining confidence that the product has not been tampered with and or for ensuring against spoilage. Additionally, peelable foils also encounter difficulty surviving sterilization without encountering problems in their removal.
A heat-fused metallic seal, which imparts a permanent seal, fused to the container is more desirable. However, the use of a conventional heat-fused foil membrane necessitates that the outer cap be removed, followed by the piercing of the membrane seal. The piercing is usually accomplished by a microbial laden device, such as a pair of scissors or a fingernail, thereby contaminating the pediatric nutritional product with bacteria.
It is thus apparent that a need exists for an improved closure for a pre-filled, membrane-sealed pediatric nutritional product containers which provides system seal integrity during retort, as well as permitting the sanitary opening of the container in a single action motion.